1. Field of the Invention
The present invention relates to an optical head device for optically recording/reproducing information on/from an information recording medium (so-called “optical disc”); more particularly, it relates to a technique for achieving a simplified and miniaturized structure and reduced manufacturing costs of an optical head device that comprises a so-called axial sliding rotating objective lens actuator and a device for correcting the inclination of the optical axis of an objective lens relative to an information recording medium. The present invention also relates to a technique for improving vibration-resisting properties of such an optical head device that comprises an axial sliding rotating objective lens actuator.
2. Description of the Background Art
FIG. 16 is a schematic diagram for explaining a structure of a conventional optical pickup device 100P; FIG. 17 is a schematic diagram for explaining the principle by which the device 100P detects the inclination of an optical disc 5P; and FIG. 18 is a schematic diagram for explaining the principle of electromagnetic drive means for rotatably driving an objective lens 4P in the device 100P. The optical pickup device 100P is disclosed, for example, in Japanese Patent Application Laid-open No. 1-263951 (1989). In this specification, an origin point O is defined on the optical disc 5P, and x, y, and z directions intersecting at right angles at the origin point O are defined.
In the conventional optical pickup device 100P, light 2P emitted from a light source 1P in the x direction is reflected by a half mirror 3P in the z direction and brought by the objective lens 4P into focus on the information recording surface of the optical disc 5P. An optical axis 9P of the objective lens 4P is generally parallel to the z direction. The light 2P is then reflected from the optical disc 5P and passes through the half mirror 3P to enter two photodetectors 21aP and 21bP in a two-segment light detector 6P. The light 2P incident on the photodetectors 21aP and 21bP is converted into an electric signal 7P, which is then used for reproduction of information or for detecting a misalignment between the objective lens 4P and the optical disc 5P.
FIG. 17 illustrates a light intensity distribution 34P when the light 2P enters the objective lens 4P, and a light intensity distribution 35P when the light 2P reflected from the inclined optical disc 5P re-enters the objective lens 4P.
In the conventional optical pickup device 100P, the objective lens 4P is held by a movable part 10P that is supported by four linear, elastic support members (e.g., metal wires) 11P mounted on a fixed member 12P.
The conventional optical pickup device 100P detects and corrects the inclination (inclination angle) of the objective lens 4P relative to the optical disc 5P as follows. First, a current responsive to a difference between outputs IaP and IbP of the photodetectors 21aP and 21bP is applied to a coil 33P, and resultant Lorentz force 43P developed between the coil 33P and magnets 41P mounted on a fixed base 16P generates a turning couple 42P. The turning couple 42P causes the movable part 10P mounting the objective lens 4P thereon to rotate on its center of gravity 40P, whereby the inclination of the objective lens 4P is corrected.
Here, the outputs IaP and IbP of the two photodetectors 21aP and 21bP are differentially computed by an operation unit 31P and applied through a power amplifier 32P to the coil 33P.
In the conventional optical pickup device 100P, as above described, the movable part 10P mounting the objective lens 4P thereon is supported only by the four wires 11P. Thus, when the optical pickup device 100P makes an access to a desired information track on the optical disc 5P, the movable part 10P vibrates widely in the direction of access. The vibrations last long as residual vibrations and it takes time to stop such vibrations. This results in an increase in access time.
Such residual vibrations can be reduced, for example, by using an optical head device comprising a so-called axial sliding rotating objective lens actuator. In the conventional axial sliding rotating method, however, the entire optical head device, including not only the objective lens actuator but also other components such as the light source, the half mirror, and the light detector, is inclined to correct the inclination of the objective lens relative to the optical disc. The above optical head device, therefore, has drawbacks of its complicated, large-scale structure and resultant high manufacturing costs.
In the axial sliding rotating objective lens actuator, both a lens holder and a support shaft inserted in a bearing hole in the lens holder are rigid bodies; therefore, disturbances such as outside vibrations and shocks are likely to be transmitted to the objective lens. From this, the above optical head device has another drawback that its operation is likely to become unstable due to disturbances.